This proposal focuses on the molecular mechanisms that underlie the guidance of specific motor neuron subtypes to their proper muscle targets. The extension and targeting of motor axons to the periphery is a fundamental component of mammalian nervous system development yet the identity of the molecules directly responsible for this process remain largely obscure. Preliminary studies indicate members of the FGF family of genes can induce motor axon outgrowth in vitro, but the effect of FGFs on motor axon guidance in vivo is unknown. The experiments in this proposal are designed is to specifically define the role of FGF genes in motor axon pathfinding. The first aim will define the expression patterns of FGFs and their receptors at embryonic stages relevant to motor axon outgrowth. Aim two will utilize FGF receptor conditional mutant mice to examine the alterations in motor axon guidance that are caused by a loss of FGF signalling. The third aim will use electroporation of chick spinal cord to asses the specificity of FGF mediated axon guidance for specifc subpopulations of motor neurons [unreadable] [unreadable]